In recent years, demands for non-contact IC cards and non-contact IC tags (hereinafter referred to as “non-contact ID”) for use in telephone cards, commuter passes, and the like have been increasing. The non-contact ID uses a radio wave for transmission/reception of data such as the residual quantity of the telephone card, and the effective limit of the commuter pass, and generates, by a radio wave outside, electric power necessary for the communication of data.
One method for producing a circuit for communication with the outside/power generation, which is so-called antenna circuit, is a printing with a conductive paste. Conductive paste of a thermosetting or thermoplastic type is printed on a resin film substrate such as polycarbonate, polyester, polyester alloy, and vinyl chloride, and is thermally cured or dried using a hot air circulation oven to form the circuit.
The thermosetting type conductive paste is required to be heated at high temperature after coating or printing on the substrate (base, or matter to be coated), since it uses as a binder a thermosetting resin such as epoxy resin, and vinyl resin and/or an inorganic substance such as glass frit. However, heat curing requires a large amount of energy, a long heating time, and a large floor area for mounting heating apparatus, and thus is not only uneconomical, but also suffers from the limitations described below.
That is, a conductive paste using as a binder an inorganic substance such as a glass frit generally needs to be fired at 800° C. or more, which is therefore not appropriate for a synthetic resin based substrate. On the other hand, a conductive paste using as a binder a thermosetting resin is applicable to a synthetic resin based substrate. The material of the resin film substrate often has, however, poor thermal resistance, and typically has a thermal deformation temperature of 120° C. or less, in view of printability, adhesiveness, laminating property, embossing workability, and costs. Accordingly, the substrate is deformed by heat curing of the paste at about 120° C. to 150° C. for 10 to 30 minutes. It becomes a serious obstacle; for example, parts placement is hindered in a subsequent step using the resultant printed wiring circuit. Specifically, the resin film substrate changes in size by as much as 0.1 to 0.5% in transverse and longitudinal directions, after the substrate is dried or cured. The change and the amount of change are not uniform in-plane, since the substrate is subjected to heat history. In extreme cases, the resin film substrate suffers unevenness, warping and wrinkling. The dimensional change is especially apparent when unwinding and winding the resin film in the form of a web (a strip or a roll). The deformation and dimensional change of the resin film substrate not only deteriorate the appearance of the resin film substrate, but also break the conductor circuit, or alter the impedance of the antenna conductor circuit, thus adversely affecting its functions. Also, there is difficulty in alignment, and a cycle time becomes prolonged when the IC chip is bonded to an electrode section of the conductor circuit to fabricate the non-contact ID.
If the condition of heat curing is at 120° C. for 30 minutes, and the resin film substrate is transported at a rate of 1 m/min, the use of a long hot air circulation oven having a length of as much as 30 m is required. Enormous space is required for its placement, and it is difficult to transport the resin film substrate stably with low tension for such a long distance at high temperatures.
The conductor circuit using the thermoplastic conductive paste is often utilized in the keyboard of a personal computer, etc. The substrate made of, for example, polyethylene terephthalate contracts in the step of drying the conductive paste. As a countermeasure, the substrate should be pretreated, i.e., annealed. Further, it requires 30 to 60 minutes to dry. The resultant conductor circuit has a defect of poor solvent resistance, etc.
An attempt has been made to form the conductor circuit with an electron beam curing type conductive paste. Using the electron beam curing type conductive paste, the substrate is heated less for curing as compared with the thermosetting or thermoplastic conductive paste, whereby the deformation of the substrate and the obstacle in the subsequent step as described above can be avoided to advantageously conduct mass production of the conductor circuits. However, the electron beam curing type conductive paste has problems, for example, in initial conductivity, and adhesiveness upon film forming.
To overcome such problems, Japanese Unexamined Patent Application Publication No. 59-173904 discloses a method for producing a conductive linear matter by irradiating an electron beam for curing, and then heating. According to this method, the cured matter has improved conductivity, but it requires heating at 100° C. to 150° C. for 5 to 60 minutes after the electron beam irradiation, which makes it difficult to apply this method to substrates having low heat resistance. Japanese Unexamined Patent Application Publication No. 2-290280 discloses a method for curing a conductive paint coated matter by irradiating an electron beam while keeping the coated matter at 50° C. or more. This method lowers the heating temperature, and decreases the adverse effects on the substrate. However, the uncured coated matter has an increased temperature and decreased viscosity depending on the paste, whereby it becomes difficult to form a fine pattern. Furthermore, the adhesiveness should be improved upon film forming.